Semiconductor light emitting device and its manufacturing method

ABSTRACT

In a semiconductor light emitting device such as a semiconductor laser using nitride III-V compound semiconductors and having a structure interposing an active layer between an n-side cladding layer and a p-side cladding layer, the p-side cladding layer is made of an undoped or n-type first layer  9  and a p-type second layer  12  that are deposited sequentially from nearer to remoter from the active layer. The first layer  9  is not thinner than 50 nm. The p-type second layer  12  includes a p-type third layer having a larger band gap inserted therein as an electron blocking layer. Thus the semiconductor light emitting device is reduced in operation voltage while keeping a thickness of the p-side cladding layer necessary for ensuring favorable optical properties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor light emitting device and itsmanufacturing method especially suitable for application tosemiconductor lasers and light emitting diodes using nitride-familyIII-V compound semiconductors.

2. Description of the Related Art

In recent years, semiconductor lasers using nitride-family III-Vcompound semiconductors such as AlGaInN and others have been a subjectof vigorous researches and developments as semiconductor lasers capableof emitting light from the blue region to the ultraviolet regionrequired for enhancing the density of optical discs, and some havealready been brought into practical use.

Semiconductor lasers having been reported heretofore include anelectron-blocking layer (also called a cap layer) made of p-type AlGaNon an active layer nearer to a p-type cladding layer (for example,Japanese Patent Laid-Open Publication No. hei 9-219556). FIG. 15 showsenergy bands, especially the conduction band, of a conventionalsemiconductor laser using the p-type AlGaN electron-blocking layer. InFIG. 15, E_(c) indicates the bottom energy in the conduction band. Inthis semiconductor laser, the p-type AlGaN electron-blocking layer isconsidered to restrict overflow of electrons and prevent separation ofIn from the active layer even during operation under a high temperatureand a high current.

In the conventional semiconductor laser, however, while the p-type AlGaNcladding layer usually has a thickness around 0.5 to 0.6 μm and an Alcomposition ratio around 0.06, the specific resistance of the p-typeAlGaN cladding layer is as high as 3 to 4 Ωcm. Therefore, a largevoltage drop occurs during operation due to the resistance of the p-typeAlGaN cladding layer, and it is difficult to control the operationvoltage not to exceed 5 V. If the p-type cladding layer is reduced inthickness, the operation voltage will certainly decrease. However, thisis not an effective countermeasure because of insufficient confinementof light, failure to obtain favorable FFP (far field pattern), and otherproblems. Additionally, since the p-type layer contains a large quantityof Mg as the p-type impurity and therefore exhibits high absorptioncoefficient to light, the p-type layer existing near the active layerincreases the internal absorption loss and degrades the laser property.

It is therefore an object of the invention to provide a semiconductorlight emitting device reduced in operation voltage and having afavorable property by appropriate design of the distance between theactive layer and the p-type layer while maintaining a thickness of thep-side cladding layer necessary and sufficient for obtaining a favorableoptical property, and to provide a method capable of easilymanufacturing such a semiconductor light emitting device.

OBJECTS AND SUMMARY OF THE INVENTION

This and other objects of the invention will appear more clearly fromthe description made below with reference to the accompanying drawings.

According to the first aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer,comprising:

-   -   the p-side cladding layer including an undraped or n-type first        layer and a p-type second layer doped with a p-type impurity        which lie in this order from one side nearer the active layer,        and the second layer including a third layer having a larger        band gap than the second layer.

This semiconductor light emitting device typically has a SCH structure(separate confinement heterostructure). That is, an n-side opticalwaveguide layer is interposed between the n-side cladding layer and theactive layer, and a p-side optical waveguide layer is interposed betweenthe p-side cladding layer and the active layer.

It is generally sufficient that the entire thickness of the p-sidecladding layer is 500˜600 nm. Thickness of the p-type second layer ofthe p-side cladding layer is typically larger than 0 nm and does notexceed 550 nm or 450 nm, but it is typically in the range from 390 to550 nm, or more typically in the range from 400 to 530 nm. On the otherhand, thickness of the undraped first layer of the p-side cladding layer(in this case, it exhibits an n⁻-type, and its specific resistance isusually lower than p-type layers approximately by one of severalfragments to one digit) is generally larger than 0 nm and does notexceed 500 nm. However, from the viewpoint of sufficiently reducing theresistance of the p-side cladding layer, it is controlled not to besmaller than 50 nm, preferably not to be smaller than 70 nm or morepreferably not to be smaller than 90 nm. On the other hand, it istypically controlled not to exceed 400 nm, 300 nm or 200 nm. Thus thethickness of the first layer may be in a range defined by a desiredcombination of those upper and lower limits. In one typical example,thickness of this first layer is in the range from 70 to 130 nm, and ina more typical example, it is controlled in the range from 90 to 110 nm.These undraped or n-type first layer and p-type second layer may be madeof a common material or different materials provided necessary opticalproperties such as sufficiently high light confining coefficient Γ andfavorable FFP are ensured. In an example of the former configuration,both the first layer and the second layer may be made of AlGaN. In anexample of the latter configuration, AlGaN may be used as the materialof the second layer whereas AlGaInN, GaN or InGaN may be used as thematerial of the first layer. The first layer and the second layer may bein direct contact, or may be in indirect contact via another layerhaving a certain function.

In case an n-side optical waveguide layer and a p-side optical waveguidelayer are provided, their thickness is larger than 0 nm and does notexceed 150 nm, in general.

The undoped or n-type first layer of the p-side cladding layerpreferably has a superlattice structure from the viewpoint offacilitating holes injected from the part of the p-side electrode duringoperation of the semiconductor light emitting device and therebyincreasing the injection efficiency, and simultaneously introducing ahetero interface to inhibit diffusion of Mg typically uses as the p-typeimpurity of the second layer to the part of the active layer and therebyprevent deterioration of the active layer. In a typical example, theentirety of the p-side cladding layer is in form of a superlatticestructure.

The third layer existing in the p-type second layer is made of a p-typenitride III-V compound semiconductor containing Al and Ga in general.More specifically, it is made of, for example p-type Al_(x)Ga_(1−x)N(where 0<x<1). From the viewpoint of effectively preventing overflow ofelectros injected to the active layer, it is preferably made of p-typeAl_(x)Ga_(1−x)N (where 0.15≦x<1).

From the viewpoint of preventing deterioration of the active layer dueto diffusion of Mg usually used as the p-type impurity of the p-typesecond layer into the active layer, distance between the active layerand the p-type second layer of the p-side cladding layer is preferablycontrolled not to be smaller than 20 nm, more preferably not to besmaller than 50 nm, or more preferably not to be smaller than 100 nm.According to a recent report, diffusion distance of holes in GaN isapproximately 0.28 μm (280 nm). Taking it into consideration, for thepurpose of reducing the probability of recombination with electrons andenhancing the injection efficiency of holes to the active layer,distance between the active layer and the p-type second layer of thep-side cladding layer is preferably controlled not to exceed thediffusion distance.

On the other hand, from the viewpoint of preventing diffusion of thep-type impurity, such as Mg, from the p-type second layer of the p-sidecladding layer to the active layer and thereby preventing deteriorationof the active layer, at least one combination of layers different inband gap or lattice constant, or at least one layer of superlatticestructure composed of layers different in atomic composition ratio, ispreferably interposed between the active layer and the p-type secondlayer of the p-side cladding layer such that it functions as a latticedistortion layer and prevents diffusion of Mg.

The first layer of the p-side cladding layer is made of AlGaN in atypical example. Especially from the viewpoint of improving thecharacteristic temperature To while preventing the threshold currentdensity J_(th) from increasing, it is preferably made of Al_(y)Ga_(1−y)Nin which the Al composition ratio is controlled not to exceed 0.04(where<0y≦0.04).

Typically, the nitride III-V compound semiconductor forming the barrierlayer of the active layer is In_(x)Ga_(1−x)N (where 0<x<1), and thenitride III-V compound semiconductor forming the well layer of theactive layer is In_(y)Ga_(1−y)N (where 0<y<1 and y>x).

A nitride III-V compound semiconductor generally contains at least onekind of group III element selected from the group consisting of Ga, Al,In and B, and one or more group V elements including at least N with orwithout additional As or P. In other words, a nitride III-V compoundsemiconductor is generally made ofAl_(x)B_(y)Ga_(1−x−y−z)In_(z)As_(u)N_(1−u−v)P_(v) (where 0≦x≦1, 0≦y≦1,0≦z≦1, 0≦u≦1, 0≦v≦1, 0≦x+y+z<1 and 0≦u+v<1). More specifically, it ismade of Al_(x)B_(y)Ga_(1−x−y−z)In_(z)N (where 0≦x≦1, 0≦y≦1, 0≦z≦1 and0≦x+y+z<1). Typically, it is made of Al_(x)Ga_(1−x−z)In_(z)N (where0≦x≦1 and 0≦z≦1). Examples of nitride III-V compound semiconductors areGaN, InN, AlN, AlGaN, InGaN, AlGaInN, and so on.

According to the second aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer,comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer, and the        first layer having a thickness not thinner than 50 nm.

In the second aspect of the invention, the foregoing explanation made inconjunction with the first aspect of the invention is also applicable tothe extent not contradictory to its nature.

According to the third aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer, and the        first layer having a thickness not thinner than 50 nm.

Basically, the above-summarized semiconductor light emitting device maybe made of any semiconductors. In addition to nitride III-V compoundsemiconductors, various kinds of III-V compound semiconductors such asAlGaAs-family semiconductors, AlGaInP-family semiconductors,InGaAsP-family semiconductors and GaInNAs-family semiconductors, II-VIcompound semiconductors such as ZnSe-family semiconductors, and evendiamond are also usable.

In the third aspect of the invention, the foregoing explanation made inconjunction with the first aspect of the invention is also applicable tothe extent not contradictory to its nature.

According to the fourth aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer andincludes a ridge structure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer, and the        second layer including a third layer having a larger band gap        than the second layer; and    -   p-type layers in opposite sides of the ridge having a thickness        in the range from 0 to 100 nm.

According to the fifth aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, and having a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer and a ridgestructure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer, and the        second layer including a third layer having a larger band gap        than the second layer; and    -   bottom surfaces of portions in opposite sides of the ridge being        deeper than the boundary between the first layer and the second        layer.

According to the sixth aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer and has aridge structure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer; and    -   p-type layers in opposite sides of the ridge having a thickness        in the range from 0 to 100 nm.

According to the seventh aspect of the invention, there is provided asemiconductor light emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer and has aridge structure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer; and    -   bottom surfaces of portions in opposite sides of the ridge being        deeper than the boundary between the first layer and the second        layer.

According to the eighth aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer and having a ridge structure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer; and    -   p-type layers in opposite sides of the ridge having a thickness        in the range from 0 to 100 nm.

According to the ninth aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer and having a ridge structure, comprising:

-   -   the p-side cladding layer including an undoped or n-type first        layer and a p-type second layer doped with a p-type impurity in        this order from one side nearer to the active layer; and    -   bottom surfaces of portions in opposite sides of the ridge being        deeper than the boundary between the first layer and the second        layer.

In the fourth, sixth and eighth aspects of the invention, for thepurpose of minimizing the thickness of the p-type second layerpositioned inside the ridge and thereby more effectively preventingleakage of the injected current outside the ridge, thickness of p-typelayers in opposite sides of the ridge is preferably controlled in therange from 0 to 50 nm. That is, even if the activation rate of thep-type impurity such as Mg in the p-type second layer is enhanced andthereby decreases the resistance of the second layer when the operationtemperature of the semiconductor light emitting device rises, since mostpart of the p-type second layer is inside the ridge, quantity of theleak current outside the ridge can be reduced significantly. Thiscontributes especially to improvement of the characteristic temperatureT₀ of a semiconductor laser.

In the fifth, seventh and ninth aspects of the invention, bottomsurfaces of portions in opposite sides of the ridge are typicallypositioned inside the first layer.

In the fourth through ninth aspects of the invention, the foregoingexplanation made in conjunction with the first to third aspects of theinvention is also applicable to the extent not contradictory to itsnature.

According to the tenth aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer, the p-side cladding layer including an undoped or n-type firstlayer and a p-type second layer doped with a p-type impurity which liein this order from one side nearer the active layer, and the secondlayer including a third layer having a larger band gap than the secondlayer, comprising:

-   -   growing layers from the active layer to the third layer in a        carrier gas atmosphere containing nitrogen as a major component        thereof and containing substantially no hydrogen.

According to the eleventh aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer, the p-side cladding layer including an undoped or n-type firstlayer and a p-type second layer doped with a p-type impurity which liein this order from one side nearer the active layer, and the first layerhaving a thickness not thinner than 50 nm, comprising:

-   -   growing layers from the active layer to the first layer of the        p-side cladding layer in a carrier gas atmosphere containing        nitrogen as a major component thereof and containing        substantially no hydrogen.

According to the twelfth aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer and have a ridge structure, the p-side cladding layer including anundoped or n-type first layer and a p-type second layer doped with ap-type impurity which lie in this order from one side nearer the activelayer, the second layer including a third layer having a larger band gapthan the second layer, and p-type layers in opposite sides of the ridgehaving a thickness in the range from 0 to 100 nm, comprising:

-   -   growing layers from the active layer to the third layer in a        carrier gas atmosphere containing nitrogen as a major component        thereof and containing substantially no hydrogen.

According to the thirteenth aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer and have a ridge structure, the p-side cladding layer including anundoped or n-type first layer and a p-type second layer doped with ap-type impurity which lie in this order from one side nearer the activelayer, the second layer including a third layer having a larger band gapthan the second layer, and bottom surfaces of portions in opposite sidesof the ridge being deeper than the boundary between the first layer andthe second layer, comprising:

-   -   growing layers from the active layer to the third layer in a        carrier gas atmosphere containing nitrogen as a major component        thereof and containing substantially no hydrogen.

According to the fourteenth aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer and have a ridge structure, the p-side cladding layer including anundoped or n-type first layer and a p-type second layer doped with ap-type impurity which lie in this order from one side nearer the activelayer, and p-type layers in opposite sides of the ridge having athickness in the range from 0 to 100 nm, comprising:

-   -   growing layers from the active layer to the first layer of the        p-side cladding layer in a carrier gas atmosphere containing        nitrogen as a major component thereof and containing        substantially no hydrogen.

According to the fifteenth aspect of the invention, there is provided amethod of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer and have a ridge structure, the p-side cladding layer including anundoped or n-type first layer and a p-type second layer doped with ap-type impurity which lie in this order from one side nearer the activelayer, and bottom surfaces of portions in opposite sides of the ridgebeing deeper than the boundary between the first layer and the secondlayer, comprising:

-   -   growing layers from the active layer to the first layer of the        p-side cladding layer in a carrier gas atmosphere containing        nitrogen as a major component thereof and containing        substantially no hydrogen.

In the tenth to fifteenth aspects of the invention, the foregoingexplanation made in conjunction with the first aspect of the inventionis also applicable to the extent not contradictory to its nature.

According to the sixteenth aspect of the invention, there is provided asemiconductor light emitting device composed of nitride III-V compoundsemiconductors and having a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer,comprising:

-   -   distance between the active layer and one of p-type layers doped        with a p-type impurity nearest to the active layer being not        less than 50 nm.

In the sixteenth aspect of the invention, for the purpose of moreeffectively preventing deterioration of the active layer by diffusion ofthe p-type impurity doped into p-type layers, distance between theactive layer and nearest one of the p-type layers is preferablycontrolled no to be smaller than 60 nm, or more preferably not to besmaller than 100 nm. For the purpose of preventing deterioration of theactive layer by diffusion of the p-type impurity, it is desirable tomaximize the distance between the active layer and the p-type layers tothe extent not inviting other difficulties. In general, it is not largerthan 500 nm. The distance between the active layer and p-type layers istypically in the range from 50 to 500 nm, or more typically in the rangefrom 100 to 200 nm. For the purpose of minimizing the internal losswhile keeping the internal quantum efficiency in a high. level, thedistance between the active layer and p-type layers is preferablycontrolled in the range from 65 to 230 nm, more preferably in the rangefrom 70 to 125 nm, and more preferably in the range from 90 to 110 nm.The p-type layer nearest to the active layer has a larger band gap thanthe p-side cladding layer, for example, which is equivalent to the thirdlayer in the first aspect of the invention. Typically, at least onelayer different in composition from the active layer and the nearestp-type layer is interposed between the active layer and this p-typelayer.

According to the seventeenth aspect of the invention, there is provideda method of manufacturing a semiconductor light emitting device composedof nitride III-V compound semiconductors to have a structure interposingan active layer between an n-side cladding layer and a p-side claddinglayer, in which the distance between the active layer and one of p-typelayers doped with a p-type impurity nearest to the active layer is notless than 50 nm, and the p-type layer nearest to the active layer has alarger band gap than the p-side cladding layer, comprising:

-   -   growing layers from the active layer to said p-type layer having        a larger band gap than the p-side cladding layer in a carrier        gas atmosphere containing nitrogen as a major component thereof        and containing substantially no hydrogen.

In the sixteenth and seventeenth aspects of the invention, the p-sidecladding layer may be entirely a p-type layer, or may be made of anundoped or n-type first layer and a p-type second layer similarly to thefirst to fifteenth aspects of the invention. In the latterconfiguration, the explanation made in conjunction with the first tofifteenth aspects of the invention is applicable to the extent notcontradictory to its nature.

In the tenth to fifteenth and seventeenth aspects of the invention, forthe purpose of effectively preventing separation of In from layerscontaining In, such as the active layer, N₂ gas atmosphere is mostpreferably used as the carrier gas atmosphere containing substantiallyno hydrogen and containing nitrogen as its major component. On the otherhand, for growth of p-type layers conducted after growth by using thecarrier gas atmosphere containing substantially no hydrogen andcontaining nitrogen as its major component, a carrier gas atmospherecontaining nitrogen and hydrogen as its major component is preferablyused for the purpose of reducing resistance values of the p-type layers.Most preferably, a mixed gas atmosphere containing N₂ and H₂ is used.

The substrate for growth of the nitride III-V compound semiconductorsmay be selected from various kinds of substrates. More specifically; inaddition to a sapphire substrate, SiC substrate, Si substrate, GaAssubstrate, GaP substrate, InP substrate, spinel substrate, silicon oxidesubstrate, and the like, those made of thick GaN and other nitride III-Vcompound semiconductor layers are also usable.

For growth of the nitride III-V compound semiconductors, varioustechniques are usable, such as metal organic chemical vapor deposition(MOCVD), hydride vapor phase epitaxial growth, halide vapor phaseepitaxial growth (HVPE), and so forth. For growth of all compoundsemiconductors including nitride III-V compound semiconductors,molecular beam epitaxy (MBE), for example, is also usable in addition tothose techniques.

In the semiconductor light emitting device according to any of the firstto ninth aspects of the invention, the p-side cladding layer is made ofthe undoped or n-type first layer and the p-type second layer. However,in a semiconductor light emitting device using as the material of then-side cladding layer a semiconductor material difficult to dope ann-type impurity and difficult to obtain a low-resistance n-typesemiconductor, it is also effective to make the n-side cladding layer ofan undoped or p-type first layer and an n-type second layer. In thiscase, the ridge is formed in the part of the n-side cladding layer.

According to the eighteenth aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer, comprising:

-   -   the n-side cladding layer including an undoped or p-type first        layer and an n-type second layer doped with an n-type impurity        in this order from one side nearer to the active layer, and the        first layer having a thickness not smaller than 50 nm.

According to the nineteenth aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer, and having a ridge structure, comprising:

-   -   the n-side cladding layer including an undoped or p-type first        layer and an n-type second layer doped with an n-type impurity        in this order from one side nearer to the active layer; and    -   n-type layers in opposite sides of the ridge having a thickness        in the range from 0 to 100 nm.

According to the twentieth aspect of the invention, there is provided asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer, and having a ridge structure, comprising:

-   -   the n-side cladding layer including an undoped or p-type first        layer and an n-type second layer doped with an n-type impurity        in this order from one side nearer to the active layer; and    -   bottom surfaces of portions in opposite sides of the ridge being        deeper than the boundary between the first layer and the second        layer.

In the eighteenth to twentieth aspects of the invention, the foregoingexplanation made in conjunction with the first to seventeenth aspects ofthe invention is also applicable to the extent not contradictory to itsnature.

According to the first to ninth aspects of the invention, since thep-side cladding layer is made of the undoped or n-type first layer andthe p-type second layer doped with a p-type impurity, which are stackedsequentially from nearer to remoter from the active layer, it ispossible to control the thickness of the p-side cladding layerdetermining optical properties such as the light confinement coefficientΓ and the p-type second layer determining the level of the operationvoltage independently from each other. Therefore, a semiconductor lightemitting device reduced in operation voltage and having favorableoptical properties (such as small θ⊥ of FPP) can be easily realized. Inother words, it is possible to minimize the thickness of p-type layerswith high specific resistance values causing an increase of theoperation voltage and thereby reduce the operation voltage while keepingthe p-side cladding layer thick enough to obtain a good light field forthe semiconductor light emitting device and thereby obtain favorableoptical properties. Additionally, since a sufficient distance can beprovided between the active layer and the second layer, diffusion of thep-type impurity of the second layer into the active layer anddeterioration of the active layer thereby can be prevented. At the sametime, internal absorption loss of the laser can be reduced, and thelaser property can be improved. Furthermore, especially when the secondlayer includes the p-type third layer having a larger band gap than thesecond layer, while the third layer prevents over flow of electronsinjected to the active layer, deterioration of the active layer can beprevented because the distance between the active layer and the thirdlayer usually having a large difference in composition from the activelayer can be designed freely and distortion generated in the activelayer can be relaxed.

According to the fourth to ninth aspects of the invention, since thethickness of n-type layers in opposite sides of the ridge is limitedwithin 0 to 100 nm, or the bottoms of the portion in opposite sides ofthe ridge are deeper than the boundary between the first layer and thesecond layer, most or all of the p-type layers including the p-typesecond layer can be formed to lie inside the ridge. Therefore, leakageof the current injected during operation of the semiconductor lightemitting device outside the ridge can be prevented effectively.

According to the tenth to fifteenth aspects of the invention, growth oflayers from the active layer to the third layer in the tenth aspect ofthe invention, or growth of layers from the active layer to the firstlayer of the p-side cladding layer in the eleventh to fifteenth aspectsof the invention, is carried out in the carrier gas atmospherecontaining substantially no hydrogen and containing nitrogen as itsmajor component. Therefore, separation of In from layers containing In,such as the active layer, can be prevented effectively. On the otherhand, p-type layers to be grown thereafter may be grown in a carrier gasatmosphere containing nitrogen and hydrogen as its major component suchthat they grow with excellent crystalline properties.

According to the sixteenth aspect of the invention, since the distancebetween the active layer and the nearest p-type layer doped with thep-type impurity is at least 50 nm, diffusion of the p-type impurity fromthe p-type layer to the active layer can be reduced significantly, anddeterioration of the active layer can be prevented.

According to the seventeenth aspect of the invention, since layers fromthe active layer to the p-side layer having a larger band gap than thep-side cladding layer are grown in the carrier gas atmosphere containingsubstantially no hydrogen and containing nitrogen as its majorcomponent, separation of In from layers containing In, such as theactive layer, can be prevented effectively, and deterioration of theactive layer can be prevented. The p-type layers to be grown thereaftermay be grown in a carrier gas atmosphere containing nitrogen andhydrogen as its major component such that they grow with excellentcrystalline properties.

According to the eighteenth to twentieth aspects of the invention, sincethe n-side cladding layer is made of the undoped or p-type first layerand the n-type second layer doped with an n-type impurity, which arestacked sequentially from nearer to remoter from the active layer, it ispossible to control the thickness of the n-side cladding layerdetermining optical properties such as the light confinement coefficientΓ and the n-type second layer determining the level of the operationvoltage independently from each other. Therefore, a semiconductor lightemitting device reduced in operation voltage and having favorableoptical properties (such as small θ⊥ of FPP) can be easily realized. Inother words, it is possible to minimize the thickness of n-type layerswith high specific resistance values causing an increase of theoperation voltage and thereby reduce the operation voltage while keepingthe n-side cladding layer thick enough to obtain a good light field forthe semiconductor light emitting device and thereby obtain favorableoptical properties. Additionally, since a sufficient distance can beprovided between the active layer and the second layer, diffusion of then-type impurity of the second layer into the active layer anddeterioration of the active layer thereby can be prevented.

Furthermore, according to the nineteenth and twentieth aspects of theinvention, since the thickness of p-type layers in opposite sides of theridge is limited within 0 to 100 nm, or the bottoms of the portion inopposite sides of the ridge are deeper than the boundary between thefirst layer and the second layer, most or all of the n-type layersincluding the n-type second layer can be formed to lie inside the ridge.Therefore, leakage of the current injected during operation of thesemiconductor light emitting device outside the ridge can be preventedeffectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a GaN compound semiconductorlaser according to the first embodiment of the invention;

FIG. 2 is a cross-sectional view showing a substantial part of the GaNcompound semiconductor laser according to the first embodiment in anenlarged scale;

FIG. 3 is a schematic diagram showing the energy band structure of theGaN semiconductor laser according to the first embodiment;

FIG. 4 is a schematic diagram showing changes of the operation voltagewith thickness of the undoped layer of the p-side cladding layer in theGaN compound semiconductor laser according to the first embodiment;

FIG. 5 is a schematic diagram showing changes of the aging deteriorationrate of with thickness of the undoped layer of the p-side cladding layerin the GaN compound semiconductor laser according to the firstembodiment;

FIG. 6 is a schematic diagram showing the optical output-to-currentproperty of the GaN compound semiconductor laser according to the firstembodiment;

FIG. 7 is a schematic diagram showing the optical output-to-currentproperty of an existing GaN compound semiconductor laser taken forcomparison with the GaN compound semiconductor laser according to thefirst embodiment;

FIG. 8 is a schematic diagram showing the energy band structure of a GaNcompound semiconductor laser according to the second embodiment of theinvention;

FIG. 9 is a schematic diagram showing the optical output-to-currentproperty of a GaN compound semiconductor laser according to the thirdembodiment of the invention;

FIG. 10 is a schematic diagram showing changes of the slope efficiencyof the GaN compound semiconductor laser according to the thirdembodiment with ambient temperature;

FIG. 11 is a schematic diagram showing the energy band structure of aGaN compound semiconductor laser according to the fourth embodiment ofthe invention;

FIG. 12 is a schematic diagram showing changes of the internal loss andthe internal quantum efficiency of a GaN compound semiconductor laseraccording to the fifth embodiment with Mg doping start position;

FIG. 13 is a schematic diagram showing changes of the threshold currentdensity of the GaN compound semiconductor laser according to the fifthembodiment with Mg doping start position;

FIGS. 14A and 14B are schematic diagrams showing changes of thecharacteristic temperature and the threshold current density of the GaNcompound semiconductor laser according to the fifth embodiment with Alcomposition of the undoped AlGaN cladding layer; and

FIG. 15 is a schematic diagram showing the energy band structure of atypical conventional GaN compound semiconductor laser.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the invention will now be explained below withreference to the drawings. In all figures showing the embodiments,common or equivalent elements are labeled with common referencenumerals.

FIG. 1 shows a GaN compound semiconductor laser according to the firstembodiment of the invention. The GaN compound semiconductor laser has aridge structure and a SCH structure. FIG. 2 is an enlarged,cross-sectional view of the ridge portion and its peripheral portion ofthe GaN compound semiconductor. FIG. 3 shows the energy bands,especially the conduction band, of the GaN compound semiconductor laser.

As shown in FIG. 1, in the GaN compound semiconductor laser according tothe first embodiment, GaN compound semiconductor layers are deposited onone major surface of a c-plane sapphire substrate 1 by a lateral crystalgrowth technique (for example, Applied Physics Letters vol. 75(1999)pp.196-198). More specifically, the GaN compound semiconductor laserincludes a stripe made of an undoped GaN buffer layer 2 bylow-temperature growth on one major surface of the c-plane sapphiresubstrate 1 and an undoped GaN compound semiconductor layer 3 on thebuffer layer 2 to form a stripe extending in the (1-100) direction.Further, an n-type GaN contact layer 4 is grown as a continuous layerfrom the undoped GaN layer 3 in the stripe as the seed crystal. Inopposite sides of the stripe, a surface portion of the c-plane sapphiresubstrate is removed as well, and the n-type GaN contact layer 4 inthese portions is configured to float from the c-plane sapphiresubstrate 1. On the n-type GaN contact layer 4, there are sequentiallyformed an n-type GaN cladding layer 5, undoped InGaN optical waveguidelayer 6 as the n-side optical waveguide layer, active layer of anIn_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N multiquantum well structure, undopedInGaN optical waveguide layer 8 as the p-side optical waveguide layer,undoped AlGaN cladding layer 9 as the p-side cladding layer, undopedcladding layer, undoped InGaN layer 10, p-type AlGaN electron-blockinglayer 11, p-type AlGaN/GaN superlattice cladding layer 12 as the p-sidecladding layer, and p-type GaN contact layer 13. The undoped InGaNoptical waveguide layer 6, undoped InGaN optical waveguide layer 8,undoped AlGaN cladding layer 9 and undoped InGaN layer 10 are n⁻-typelayers. The purpose of using the p-type AlGaN/GaN superlattice claddinglayer 12 as the p-side cladding layer is to permit holes to pass throughmore easily by tunneling.

Thickness of the undoped GaN buffer layer 2 is 30 nm for example. Theundoped GaN layer 3 is 2 μm thick for example. The n-type GaN contactlayer 4 is 4 μm for example, and it is doped with silicon (Si) forexample as its n-type impurity. The n-type AlGaN cladding layer 5 is 1,2μm thick for example, and doped with Si for example as its n-typeimpurity. Its Al composition ratio may be 0.065 for example. The undopedInGaN optical waveguide layer 6 is 30 nm thick for example, and its Incomposition ratio is 0.02 for example. The active layer 7 having theundoped In_(x)Ga_(1−x)N/In_(y)Ga_(1−y)N multiquantum well structure is amulti-layered film made by alternately stacking In_(x)Ga_(1−x)N layersas barrier layers and In_(y)Ga_(1−y) N layers as well layers. Forexample, thickness of each In_(x)Ga_(1−x)N layer as the barrier layermay be 7 nm, and x=0.02, for example. Thickness of each In_(y)Ga_(1−y) Nlayer may be 3.5 nm, y=0.08, and the number wells is 3, for example.

The undoped InGaN optical waveguide layer 8 is 30 nm thick, for example,and its In composition ratio is 0.02, for example. The undoped AlGaNcladding layer 9 is 100 nm thick, for example, and its Al compositionratio is 0.025, for example. The undoped InGaN layer 10 is 5 nm thick,for example, and its In composition ration is 0.02, for example. Thep-type AlGaN electron blocking layer 11 is 10 nm thick, for example, andits Al composition ratio is 0.18, for example. The p-type AlGaN/GaNsuperlattice cladding layer 12 may include 2.5 nm thick undoped AlGaNlayers as barrier layers and 2.5 nm thick, Mg-doped GaN layers as welllayers, which are alternately stacked. Thus, the average Al compositionratio is 0.06 for example, and the total thickness is 400 nm, forexample. The p-type GaN contact layer 11 is 100 nm thick, for example,and Mg, for example, is doped as its p-type impurity.

The upper part of the n-type GaN contact layer 4 and other overlyinglayers make the form of a mesa of a predetermined width as a whole. Inthis mesa portion, the p-type AlGaN/GaN superlattice cladding layer 12and the p-type GaN contact layer 13 make a ridge 14 extending in the<1-100> orientation, for example. Width of this ridge 14 is 1.6 μm, forexample. This ridge, which is the laser stripe portion, is located in alow defective region between the transition 15 propagating from the seedcrystal for lateral crystal growth and the associating portion oflateral growth from adjacent seed crystals.

In this case, the total thickness d (FIG. 2) of the p-type layers inopposite sides of the ridge 14, namely the p-type AlGaN electronblocking layer 11 and the p-type AlGaN/GaN cladding layer 12 in thisexample, is in the range from 0 to 100 nm, or preferably in the rangefrom 0 to 50 nm.

In form of covering the entirety of the mesa portion, an insulatinglayer 17 such as 40 nm thick SiO₂ film, for example, and a 45 nm thickSi film 18, for example, are formed sequentially. The insulating film 17is used for electrical insulation and protection of the surface. The Sifilm 18 is used for enhancing the absorption coefficient of the primarymode of laser light, which may invite kink phenomenon, in the sidewallportions of the ridge 14. The insulating film 17 and the Si film 18 havean opening 19 in the location above the ridge 14, and the p-sideelectrode 20 contacts the p-type GaN contact layer 13 through theopening 19. The p-side electrode 20 has a structure made by sequentiallystacking a Pd film, Pt film and Au film, which may be 10 nm thick, 100nm thick and 300 nm thick, respectively. On the other hand, theinsulating film 17 and the Si film 18 have another opening 21 in apredetermined location adjacent the mesa portion, and the n-sideelectrode 22 contacts the n-type GaN contact layer 4 through the opening21. The n-side electrode 22 has a structure made by sequentiallystacking a Ti film, Pt film and Au film, which may be 10 nm thick, 50 nmthick and 100 nm thick, respectively.

Next explained is a method of manufacturing the GaN compoundsemiconductor laser according to the first embodiment.

First prepared is a c-plane sapphire substrate 1 with a surface cleanedby thermal cleaning, for example. Then the undoped GaN buffer layer 2 isgrown on the c-plane sapphire substrate 1 by metal organic chemicalvapor deposition (MOCVD) at a temperature around 500° C., for example.Thereafter, the undoped GaN layer 3 is grown again by MOCVD at thegrowth temperature of 1000° C., for example.

After that, a SiO₂ film (not shown), 100 nm thick for example, is formedon the entire surface of the undoped GaN layer 3 by CVD, vacuumevaporation or sputtering, for example. Then a resist pattern (notshown) of a predetermined configuration is formed on the SiO₂ film bylithography. Next using this resist pattern as a mask, the SiO₂ film isselectively etched and patterned by wet etching using a hydrofluoricacid-based etching liquid, or RIE using a gas containing fluorine suchas CF₄ or HF₃. Next using the SiO₂ film having the predeterminedconfiguration as a mask, the underlying layers are selectively etched byRIE, for example, until the top portion of the c-plane sapphiresubstrate 1 is removed. In this RIE, a chlorine-based gas may be used asthe etching gas. As a result of the etching, the undoped GaN layer 3 asthe seed crystal is made out in form of a stripe. The extendingdirection of the stripe-shaped undoped GaN layer 3 is the <1-100>direction.

In the next process, the SiO₂ film used as the etching mask is removed,and the n-type GaN contact layer 4 is grown from the stripe-shapedundoped GaN layer 3 as the seed crystal by the aforementioned lateralcrystal growth technique. The growth temperature in this process may be1070° C. for example.

Subsequently, the n-type AlGaN cladding layer 5, undoped InGaN opticalwaveguide layer 6, active layer 7 having the undopedGa_(1−x)In_(x)N/Ga_(1−y)In_(y)N multiquantum well structure, undopedInGaN optical guide layer 8, undoped AlGaN cladding layer 9, undopedInGaN layer 10, p-type AlGaN electron blocking layer 11, p-typeAlGaN/GaN superlattice cladding layer 12 and p-type GaN contact layer 13are sequentially grown on the n-type GaN contact layer 4 by MOCVD. Forgrowth of these layers, the temperature is adjusted to, for example,900˜1000° C. for the n-type AlGaN cladding layer 5, 780° C. from theundoped InGaN optical waveguide layer 6 to the p-type AlGaN electronblocking layer 11, and 900˜1000° C. for the p-type AlGaN/GaNsuperlattice cladding layer 12 and the p-type GaN contact layer 13.

Materials for growth of these GaN compound semiconductor layers may be,for example, trimethyl gallium ((CH₃)₃Ga, TMG) as the material of Ga,trimethyl aluminum ((CH₃)₃Al, TMA) as the material of Al, trimethylindium ((CH₃)₃In, TMI) as the material of In and NH₃ as the material ofN. Dopants may be, for example, silane (SiH₄) as the n-type dopant, andbis=methylcyclopentadienile magnesium (CH₃C₅H₄)₂Mg) orbis=cyclopentadienile magnesium ((CH₅H₅)₂Mg) as the p-type dopant.

Carrier gas atmospheres during growth of these GaN compoundsemiconductor layers may be, for example, a mixture gas of N₂ and H₂ forthe n-type GaN contact layer 4 and the n-type AlGaN cladding layer 5, N₂gas atmosphere from the undoped InGaN optical waveguide layer to thep-type AlGaN electron blocking layer 11, and mixture gas of N₂ and H₂for the p-type AlGaN/GaN superlattice cladding layer 12 and the p-typeGaN contact layer 13. In this case, for growth of the layers from theundoped InGaN optical waveguide layer 6 to the p-type AlGaN electronblocking layer 11, N₂ gas atmosphere is used as the carrier gasatmosphere, and the carrier gas atmosphere does not contain H₂.Therefore, separation of In from the undoped InGaN optical waveguidelayer 6, active layer 7, undoped InGaN optical waveguide layer 8 andundoped InGaN layer 10 can be prevented, and these layers can beprotected from deterioration. Additionally, since the mixture gas of N₂and H₂ is used as the carrier gas atmosphere during growth of the p-typeAlGaN/GaN superlattice cladding layer 12 and the p-type GaN contactlayer 13, these p-type layers can be grown to have good crystallineproperties.

In the next process, the c-plane sapphire substrate having those GaNcompound semiconductor layers grown thereon as explained above isremoved from the MOCVD apparatus. Then, after a SiO₂ film, 0.1 μm thickfor example, is formed on the entire surface of the p-type GaN contactlayer 13 by CVD, vacuum evaporation or sputtering, for example, a resistpattern (not shown) of a predetermined configuration corresponding tothe shape of the mesa portion is formed on the SiO₂ film by lithography.Next using this resist pattern as a mask, the SiO₂ film is selectivelyetched and patterned by wet etching using a hydrofluoric acid-basedetching liquid, or RIE using a gas containing fluorine such as CF₄ orHF₃. Next using the SiO₂ film having the predetermined configuration asa mask, the underlying layers are selectively etched by RIE, forexample, to a depth reaching the n-type GaN contact layer 4. In thisRIE, a chlorine-based gas may be used as the etching gas. As a result ofthe etching, upper part of the n-type GaN contact layer 4, n-type AlGaNcladding layer 5, undoped InGaN optical waveguide layer 6, active layer7, undoped InGaN optical waveguide layer 8, undoped AlGaN cladding layer9, undoped InGaN layer 10, p-type AlGaN electron blocking layer 11,p-type AlGaN/GaN superlattice cladding layer 12 and p-type GaN contactlayer 13 are patterned to the form of a mesa.

In the next process, after the SiO₂ film used as the etching mask isremoved, a SiO₂ film (not shown), 0.2 μm thick for example, is formedagain on the entire substrate surface by CVD, vacuum evaporation orsputtering, for example. After that, a resist pattern (not shown) of apredetermined configuration corresponding to the ridge portion is formedon the SiO₂ film by lithography. Next using this resist pattern as amask, the SiO₂ film is selectively etched to a pattern corresponding tothe ridge portion by wet etching using a hydrofluoric acid-based etchingliquid, or RIE using a gas containing fluorine such as CF₄ or HF₃.

In the next process, using the SiO₂ film as a mask, etching is carriedout by RIE until the total thickness of the remaining p-type AlGaN/GaNsuperlattice cladding layer 12 and the p-type AlGaN electron blockinglayer 11 falls in the range from 0 to 100 nm or preferably in the rangefrom 0 to 50 nm to make out the ridge 14. In this RIE, a chlorine-basedgas may be used as the etching gas.

In the next process, the SiO₂ film used as the etching mask is removed,and the insulating film 17 such as SiO₂ film and the Si film 18 aresequentially formed on the entire substrate surface by CVD, vacuumevaporation or sputtering, for example.

In the next process, a resist pattern (not shown) is formed bylithography to cover the surface of the Si film 18 in the regionexcluding the region for making the n-side electrode.

Next using this resist pattern as a mask, the Si film 18 and theinsulating film 17 are selectively etched to make the opening 21.

In the next process, while maintaining the resist pattern, a Ti film, Ptfilm and Au film are sequentially deposited on the entire substratesurface by vacuum evaporation, for example. Thereafter, the resistpattern and the overlying Ti film, Pt film and Au film are removedtogether (lift-off). As a result, the n-side electrode 22 in contactwith the n-type GaN contact layer through the opening 21 in theinsulating film 17 and the Si film 18 appears. Thereafter, alloying iscarried out to bring the n-side electrode 22 into ohmic contact.

Thereafter, through similar processes, the Si film 18 and the insulatingfilm 17 are removed from above the ridge 14 by etching to form anopening 19. Thereafter, similarly to the n-side electrode 22, the p-sideelectrode 20 having the Pd/Pt/Au structure in contact with the p-typeGaN contact layer through the opening 19 is formed.

After that, the substrate having formed the laser structure through theforegoing steps is processed to bars by cleavage or the like to formopposite cavity edges, and after coating these cavity edges, each bar isdivided to chips by cleavage or the like.

As a result, the intended GaN compound semiconductor laser having theridge structure and the SCH structure is completed.

With this GaN compound semiconductor laser, thickness t of the undopedAlGaN cladding layer 9 in the p-side cladding layer made of the undopedAlGaN cladding layer 9 and the p-type AlGaN/GaN superlattice claddinglayer 12 was changed. A result of examining corresponding operationvoltage values and aging deterioration rates are shown in FIG. 5. Theseoperation voltage values were obtained at 25° C. under the opticaloutput of 30 mW. The aging deterioration rates were obtained at 60° C.under the optical output of 30 mW. Since the rising rate of theoperation current I_(op) is high immediately after the start of aging,rising rates of I_(op) from 100 to 300 hours were employed. The initialoperation current I_(op) was 55 mA. the specific resistance of theundoped AlGaN cladding layer 9 is around one of several parts of 1 Ωcm,and the specific resistance of the p-type AlGaN/GaN superlatticecladding layer 12 is around 2 Ωcm. The cavity length was 600 μm (0.06cm), width of the ridge 14 was 1.6 μm, and the entire thickness of thep-side cladding layer was 500 nm. TABLE 1 Operation Aging Deteriorationt (nm) Voltage (V) Rate (%) 0 5.13 5.50 20 5.08 2.50 50 4.99 1.10 1004.85 1.00 150 4.70 1.30 200 4.56 1.70 250 4.42 2.10 300 4.27 2.20 3504.13 2.30 400 3.99 2.70

If the operation voltage under 30 mW (25° C.) is preferably not higherthan 5 V, and the aging deterioration rate is considered to be in apractical level when the rising rate of the operation current is nothigher than 20% after operation of 3000 hours, it is understood fromTable 1, FIGS. 4 and 5 that the thickness of the undoped AlGaN claddinglayer 9 must be at least 50 nm to satisfy those conditions. Further, thethickness of the undoped AlGaN cladding layer 9 is preferably in therange from 50 to 250 nm from the viewpoint of the aging deteriorationrate.

Changes of the optical output to current property of the GaN compoundsemiconductor laser were measured by changing the environmentaltemperature by 10° C. from 20° C. to 80° C. A result of the measurementis shown in FIG. 6. For comparison purposes, a result of similarmeasurement with an existing GaN compound semiconductor laser developedby the same Inventor (Paper for 48th Lecture of Applied Physics RelatedUnion, 28p-E-12(2001), p.369) is shown in FIG. 7. It is appreciated fromFIG. 6 that the characteristic temperature T₀ of this GaN compoundsemiconductor laser is 235 K. However, it is appreciated from FIG. 7that the characteristic temperature of the existing GaN compoundsemiconductor laser is 146 K. That is, the characteristic temperature Toof this GaN compound semiconductor laser is higher than that of theexisting GaN semiconductor laser by as much as 90 K. The value 235 K asthe characteristic temperature T₀ is a significantly high value that wasimpossible to obtain even with semiconductor lasers of other compounds.Additionally, when FIG. 6 is compared with FIG. 7, it is appreciatedthat the inclination of the optical output to current characteristic,which is the slope efficiency, of this GaN compound semiconductors isconsiderably higher than that of the existing GaN compound semiconductorlaser.

According to the first embodiment, the following various advantages areensured. Since the p-side cladding layer is made of the undoped AlGaNcladding layer 9, 105 nm thick for example, and the p-type AlGaN/GaNsuperlattice cladding layer 12, 400 nm thick for example, in this orderfrom one side nearer to the active layer 7, the operation voltage of theGaN compound semiconductor laser can be reduced by approximately 0.16 Vfrom that of a structure in which the entirety of the p-side claddinglayer is the p-type AlGaN/GaN cladding layer 12. Additionally, since theentire p-side cladding layer is approximately 500 nm thick andsufficiently thick, light can be sufficiently confined in the p-side,and favorable FFP can be obtained. That is, the operation voltage can bereduced by decreasing the thickness of the p-type AlGaN/GaN superlatticecladding layer 12 causing an increase of the operation voltage by thethickness as large as 100 nm while maintaining the thickness of thep-side cladding layer necessary for obtaining favorable opticalcharacteristics.

Additionally, since the distance from the active layer 7 to the Mg-dopedp-type layers, i.e. the p-type AlGaN electron blocking layer 11, p-typeAlGaN/GaN superlattice cladding layer 12 and p-type GaN contact layer13, is as large as the total thickness of the undoped InGaN opticalwaveguide layer 8, undoped AlGaN cladding layer 9 and undoped InGaNlayer 10, which may be 30 nm+100 nm+5 nm=135 nm, diffusion of Mg fromthe p-type layers into the active layer 7 can be prevented efficientlyduring crystal growth or aging, for example, and the active layer 7 canbe prevented from deterioration caused by diffusion of Mg. As a result,the aging deterioration rate of the GaN compound semiconductor layer canbe reduced, and the reliability and the production yield can beimproved.

Further, since the undoped AlGaN cladding layer, which is a latticedistortion layer, exists between the active layer and Mg-doped p-typelayers, this also contributes to preventing diffusion of Mg from thep-type layers into the active layer and to more effectively preventingthe active layer 7 from deterioration.

Furthermore, since Mg-doped p-type layers in general are inferior incrystalline property to n-type layers and are liable to sufferabsorption of light, if the p-type layers are located near the activelayer 7, the light absorption coefficient a will increase. In thisembodiment, however, since the p-type layers are distant from the activelayer 7 by as much as 135 nm, α near the active layer 7 can be keptsufficiently low. As a result, the threshold current density J_(th) ofthe GaN compound semiconductor laser and hence the threshold currentI_(th) can be reduced, and the slope efficiency can be improvedsimultaneously. Additionally, since the Mg-doped p-type layers not goodin crystalline property are sufficiently distant from near the activelayer 7 having a high density of light, crystals near the active layer 7are not deteriorated so much by light, and the GaN compoundsemiconductor laser can be enhanced in lifetime and reliability.

Moreover, although there is a large difference of lattice constantbetween the p-type AlGaN electron blocking layer 11 having the Alcomposition ratio as large as 0.18 and the active layer 7 made of InGaNlayers, since they are distant by as much as 135 nm, distortiongenerated in the active layer 7 by the lattice constant difference canbe relaxed, and the emission efficiency can be improved accordingly.This results in improving the quantum efficiency, decreasing thethreshold current density J_(th) and hence the threshold current I_(th),and improving the slope efficiency.

Further, since the undoped InGaN layer 10 having the lattice constantsubstantially equal to that of the active layer is interposed betweenthe undoped AlGaN cladding layer 9 and the p-type AlGaN electronblocking layer 11, even if there is a large difference between thelattice constant of the active layer and the lattice constants of thep-type AlGaN electron blocking layer 11 and the p-type AlGaN/GaNsuperlattice cladding layer 12, distortion generated in the active layer7 due to the p-type AlGaN electron blocking layer 11 and the p-typeAlGaN/GaN superlattice cladding layer 12 can be relaxed. Thiscontributes to reducing the threshold current density J_(th) and hencethe threshold current I_(th) of the GaN compound semiconductor laser andimproving the slope efficiency.

Reduction of the threshold current I_(th) further leads to improvementof the noise property of the GaN compound semiconductor laser.

When electrons injected into the active layer run through the activelayer 7 and reach the undoped AlGaN cladding layer 9, some electronshaving energies larger than the energy difference ΔE_(c) (FIG. 3) of theconduction band between the undoped InGaN optical waveguide layer 8 andthe undoped AlGaN cladding layer 9 lose energies corresponding to ΔE_(c)when they jump over the undoped AlGaN cladding layer 9. The otherelectrons originally having energies smaller than ΔE_(c) cannot jumpover the undoped AlGaN cladding layer 9 and remain in the undoped InGaNoptical waveguide layer 8. Since the energy and number of electronstending to jump over the undoped AlGaN cladding layer 9 decrease, theslope efficiency of the GaN compound semiconductor laser can beimproved. It is also possible to prevent overflow of electrons duringhigh-temperature, high-output driving of the GaN compound semiconductorlaser and to reduce the operation current and operation voltage of theGaN compound semiconductor laser.

Most part of the p-type layers is positioned inside the ridge 14, andthe p-type layers existing outside the ridge 14 are limited to thep-type AlGaN/GaN superlattice cladding layer 12 having a total thicknesswithin 100 nm or preferably within 50 nm and the 10 nm thick p-typeAlGaN electron blocking layer 11. Thus they are sufficiently thin andtheir lateral resistance is sufficiently high. Therefore, even when theoperation temperature of the GaN compound semiconductor laser rises andresults in lowering the resistance of those p-type layer due toactivated Mg therein, the current leaking to opposite sides of the ridge14 is very small. This contributes to remarkably increasing thecharacteristic temperature T₀ of the GaN compound semiconductor laser toas high as 236K. Furthermore, the existing GaN compound semiconductorlaser using only p-type layers as all of the p-side cladding layersneeds considerably deep etching for making the ridge when it is intendedto reduce the thickness of the p-type layers in opposite sides of theridge, and if they are etched deeply, the difference An in refractionindex increases between the inside and outside the ridge, and kinks willeasily occur. Further, the p-type layers are deeply etched by RIE,plasma damage occurs in the active layer 7, and it may deteriorate thecharacteristics of the GaN compound semiconductor laser. In contrast,the GaN compound semiconductor laser according to the instant embodimentis free from those problems even when the depth of the ridge 14 isequivalent to that of the existing GaN compound semiconductor laser, andcan adjust the thickness of the p-type layers in opposite sides of heridge 14 not to exceed 100 nm or preferably not to exceed 50 nm asexplained above.

Since the activation energy of holes in the p-type AlGaN electronblocking layer 11 is high, most of holes are inactive at roomtemperatures. However, as the temperature increases, holes areactivated, and the electron blocking effect of the p-type AlGaN electronblocking layer is enhanced. It is presumed that this effect wasdifficult to ascertain in the existing GaN compound semiconductor laserbecause a large quantity of current leaked to opposite sides of theridge. In the GaN compound semiconductor laser, however, the quantity ofthe leak current to opposite sides of the ridge 14 is vary small asexplained above, the electron blocking effect by the p-type AlGaNelectron blocking layer 11 is high, and electrons are effectivelyprevented from overflow even during high-temperature, high-outputdriving.

Above-mentioned reduction of the leak current, i.e. the useless current,during high-temperature driving contributes to reducing the thresholdcurrent I_(th) and to realizing a GaN compound semiconductor laser withlow noise even at high temperatures.

The above-explained remarkable improvement of the characteristicstemperature T₀ enables improvement of the so-called droopcharacteristic. The droop characteristic is an important parameter forapplication of the GaN compound semiconductor laser to a light source oflaser beam printer or the like. Even when a plurality of GaN compoundsemiconductor lasers are integrated closely on a common substrate, sincethe GaN compound semiconductor lasers have a very high characteristictemperature T₀, thermal cross talk among the GaN compound semiconductorsis minimized. Therefore, the GaN compound semiconductor laser accordingto the instant embodiment is suitable for use in a multi-beam laser aswell.

Since the undoped AlGaN cladding layer 9 forms a part of the p-sidecladding layer, less p-type layers exist as a whole in the p-side of theactive layer 7, and the probability that electrons overflowing from theactive layer 7 are trapped into recombination centers and run tonon-emitting recombination is small. Assuming that the probability ofelectrons being trapped in p-type layers increases as the temperatureincreases, this structure of GaN compound semiconductor laser will beeffective for reducing useless current.

Since the carrier gas atmosphere used for growth of the layers from theundoped InGaN optical waveguide layer to the p-type AlGaN electronblocking layer 11 is N₂ atmosphere, and does not contain H₂, separationIn especially from the active layer 7 is prevented, and deterioration ofthe active layer 7 is prevented. Therefore, the GaN compoundsemiconductor laser is improved in reliability and lifetime.

Thus the first embodiment can realize a GaN compound semiconductor laserlow in operation voltage and threshold current, excellent in temperaturecharacteristic, and having a long lifetime and high reliability.

The GaN compound semiconductor laser according to the first embodiment,reduced in operation current and operation voltage duringhigh-temperature, high-output driving, and having a long lifetime, issuitable for use as a high-throughput semiconductor laser for writingespecially with an optical disc.

Next explained is a GaN compound semiconductor laser according to thesecond embodiment of the invention. FIG. 8 shows the energy bandstructure of this GaN compound semiconductor laser.

As shown in FIG. 8, the GaN semiconductor compound semiconductor laseraccording to the second embodiment includes an undoped AlGaN/GaNsuperlattice cladding layer 23 in lieu of the undoped AlGaN claddinglayer 9 used in the GaN compound semiconductor laser according to thefirst embodiment. The undoped AlGaN/GaN superlattice cladding layer 23includes 2.5 nm thick undoped AlGaN layers as barrier layers and 2.5 nmthick GaN layers as well layers, for example, which are alternatelystacked. The average Al composition ratio of this cladding layer 23 is0.025˜0.10, for example, and its entire thickness is 100˜500 nm, forexample. In the other respects, configuration of the GaN compoundsemiconductor laser according to the first embodiment is the same asthat of the first embodiment. So its explanation is omitted.

According to the second embodiment, since the undoped layer among p-sidecladding layers is the undoped AlGaN/GaN superlattice cladding layer 23,holes injected from the part of the p-side electrode 20 and havingreached the undoped AlGaN/GaN superlattice cladding layer 23 easily passthrough the undoped AlGaN/GaN superlattice cladding layer 23 by thetunneling effect and are injected to the active layer 7. Therefore,injection of holes into the active layer 7 is easier, and the operationvoltage of the GaN compound semiconductor laser is still furtherreduced. In addition, hetero interfaces existing in the undopedAlGaN/GaN superlattice cladding layer 23 effectively prevent diffusionof Mg from the p-type layers into the active layer 7, and effectivelyprevents deterioration of the active layer 7. Other advantages of thesecond embodiment are common to those of the first embodiment.

Next explained is a GaN compound semiconductor laser according to thethird embodiment of the invention.

The GaN semiconductor compound semiconductor laser according to thethird embodiment basically has the same structure as the GaN compoundsemiconductor laser according to the first embodiment. However, theundoped InGaN optical waveguide layer 8 and the p-type AlGaN/GaN superlattice cladding layer 12 are different in thickness from those in theGaN compound semiconductor laser according to the first embodiment. Morespecifically, in the GaN compound semiconductor according to the firstembodiment, the undoped InGaN optical waveguide layer 8 is 30 nm thickand the p-type AlGaN/GaN superlattice cladding layer 12 is 400 nm thick,for example. In the GaN compound semiconductor laser according to thethird embodiment, the undoped InGaN optical waveguide layer 8 is 24.5 nmthick and the p-type AlGaN/GaN superlattice cladding layer 12 is 500 nmthick, for example. In the other respects, the GaN compoundsemiconductor laser taken here is common to the GaN compoundsemiconductor laser according to the first embodiment. So itsexplanation is omitted.

Changes of the optical output to current property of this GaN compoundsemiconductor laser were measured by changing the environmentaltemperature by 10° C. from 20° C. to 80° C. A result of the measurementis shown in FIG. 9. It is appreciated from FIG. 9 that thecharacteristic temperature T₀ of this GaN compound semiconductor laseris 230 K. By comparison of FIG. 9 with FIG. 7, gradient of the opticaloutput to current property, i.e. sloping efficiency, of this GaNcompound semiconductor laser is considerably larger than that of theexisting GaN compound semiconductor laser.

FIG. 10 shows measured changes of the slope efficiency of this GaNcompound semiconductor laser by the environmental temperature. Forcomparison purposes, FIG. 10 also shows a result of similar measurementwith the existing GaN compound semiconductor laser. It is appreciatedfrom FIG. 10 that, while the slope efficiency of the existing GaNcompound semiconductor laser continuously decreases as the environmentaltemperature rises, the slope efficiency of the GaN compoundsemiconductor laser according to the third embodiment increase as theenvironmental temperature rises from room temperatures approximately to40° C. and remain constant above that temperature. This relies on thereason already explained. That is, in the existing GaN compoundsemiconductor laser, the electron blocking effect by the p-type AlGaNelectron blocking layer was difficult to ascertain because of a largequantity of the leak current to opposite sides of the ridge; however, inthe GaN compound semiconductor laser according to the third embodiment,because of remarkable reduction of the leak current to opposite sides ofthe ridge 14, the electron blocking effect by the p-type AlGaN electronblocking layer 11 is high, and overflow of electrons is effectivelyprevented even during high-temperature, high-output driving.

This third embodiment has the same advantages as those of the firstembodiment.

Next explained is a GaN compound semiconductor laser according to thefourth embodiment of the invention. FIG. 11 shows the energy bandstructure, especially its conduction band, of this GaN compoundsemiconductor laser.

As shown in FIG. 11, in the GaN semiconductor compound semiconductorlaser according to the fourth embodiment, the p-type AlGaN electronblocking layer 11 is positioned in the p-type AlGaN/GaN superlatticecladding layer 12. Although the GaN compound semiconductor laseraccording to the first embodiment is configured to interpose the p-typeAlGaN electron blocking layer 11 between the undoped InGaN layer 10 andthe p-type AlGaN/GaN superlattice cladding layer 12, but the GaNcompound semiconductor laser according to the fourth embodiment locatesthe p-type AlGaN electron blocking layer 11 inside the p-type AlGaN/GaNsuperlattice cladding layer 12 apart from the undoped InGaN layer 10.Thickness of the p-type AlGaN/GaN superlattice cladding layer 12 betweenthe undoped AlGaN cladding layer 9 and the p-type AlGaN electronblocking layer 11 may be around 10˜50 nm, for example. The otherconfiguration of this GaN compound semiconductor laser is common to thatof the first embodiment.

The same method as that of the first embodiment is used formanufacturing the GaN compound semiconductor laser according to thisembodiment. Its explanation is omitted here.

This fourth embodiment also has the same advantages as those of thefirst embodiment.

Next explained is a GaN compound semiconductor laser according to thefifth embodiment of the invention.

The GaN semiconductor compound semiconductor laser according to thefifth embodiment basically has the same structure as the GaN compoundsemiconductor laser according to the first embodiment; however, it ischaracterized in that the distance D (see FIG. 3) between one endsurface of the well layer of the active layer 7 nearest to the undopedInGaN optical waveguide layer 8 and one end surface of the p-type AlGaNelectron blocking layer nearer to the active layer 7, which is theMg-doping start position, is 65˜230 nm and that Al composition ratio zof the undoped AlGaN cladding layer 9 is 0<z≦0.04. The other features ofthis GaN compound semiconductor laser are common to those of the fistembodiment.

Here again, the same method as that of the first embodiment is used formanufacturing the GaN compound semiconductor laser according to thisembodiment. Its explanation is omitted here.

FIG. 12 shows a result of measurement to examine how the internalquantum efficiency η₁ and the internal loss α₁ of this GaN compoundsemiconductor layer change with D, which is the MG-doping startposition. As shown in FIG. 12, as D increases, that is, as the Mg-dopingstart position becomes far away from the active layer 7, α₁ goes ondecreasing, but η₁ largely decreases stepwise. When designing lasers, itis desirable to decrease α₁ while maintaining η₁ at a high value.

In FIG. 12, α₁ is substantially constant in the region of D>230 nmregardless of D. There is no point in further increase of D fordecreasing α₁, and it only increases the time required for epitaxialgrowth and decreases the productivity. Therefore, D is preferablylimited within 230 nm. On the other hand, although η_(l) is around 0.96regardless of D, it slightly decreases when D increases, then rapidlydecreases after D exceeds approximately 110 nm until reaching 140 nm,and keeps 0.8 in the region of D>140 nm. In the region where η₁ does notdecrease, D had better be largest from the viewpoint of reducing α₁.Therefore, D is preferably not smaller than 65 nm.

From the foregoing review, D is preferably in the range from 65 nm to230 nm. In this range of D, η₁ is 0.8 or more, and α₁ is 20 cm⁻¹ orless. These are sufficiently practical levels. When D is in the range of70 to 125 nm, η₁ is 0.9 or more, and α₁ is 19 cm⁻¹ or less. These valuesare more preferable. When D is in the range of 90 to 110 nm, η₁ is 0.95or more, and α₁ is 15 cm⁻¹ or less. These values are still morepreferable.

FIG. 13 shows a result of measurement conducted to examine how thethreshold current density J_(th) of the GaN compound semiconductor laseraccording to the fifth embodiment changes with D, which is the Mg-dopingstart position. As shown in FIG. 13, in the region of D from 65 to 230nm, the threshold current density J_(th) is lowest. It is appreciatedtherefore that optimum values of D fall in the range from 65 to 230 nmalso from the viewpoint of the threshold current density J_(th). FIGS.14A and 14B show changes of the characteristic temperature T₀ (FIG. 14A)and the threshold current density J_(th) (FIG. 14B) of the GaN compoundsemiconductor laser according to the fifth embodiment when changing theAl composition of the undoped AlGaN cladding layer 9 while fixing D in136.5 nm and the thickness of the undoped AlGaN cladding layer 9 in 100nm. It is appreciated from FIGS. 14A and 14B that T₀ rises as the Alcomposition of he undoped AlGaN cladding layer 9 increases but thethreshold current density J_(th) at 20° C. also increases (J_(th)@20°C.). This phenomenon is assumed to occur because the increase of the Alcomposition of the undoped AlGaN cladding layer 9 degrades the injectionefficiency of holes into the active layer 7. Enhancement of thetemperature characteristic is advantageous for controlling the increaseof the threshold current during high-temperature driving. However, theincrease of the threshold current degrades the efficiency of improvingthe temperature characteristics during low-temperature driving. It canbe known from the threshold current density J_(th) (J_(th)@50° C.) thatthe Al composition is desirable to be not larger than 4%.

As reviewed above, in addition to the same advantages as those of thefirst embodiment, the fifth embodiment can realize a GaN compoundsemiconductor laser more excellent in laser property, which is capableof keeping the internal quantum efficiency η₁ sufficiently high, theinternal loss α₁ sufficiently low, the characteristic temperature T₀high and the threshold current density low.

Heretofore, specific embodiments of the invention have been explained.However, the invention is not limited to these embodiments butcontemplates various changes and modifications based on the technicalconcept of the invention.

For example, numerical values, structures, configurations, substrates,source materials, processes, and so on, are not but mere examples, andother numerical values, structures, configurations, substrates, sourcematerials, processes, etc. may be acceptable.

For example, although the first to fifth embodiments have been explainedas first depositing n-type layers of the laser structure on thesubstrate and thereafter depositing p-type layers thereon, the order ofdeposition may be contrary to first deposit p-type layers on thesubstrate and then deposit n-type layers.

Further, the undoped InGaN optical waveguide layer 6 as the n-sideoptical waveguide layer and the undoped InGaN optical waveguide layer 8as the p-side optical waveguide layer are equal in composition in thefirst to fifth embodiments. However, the undoped InGaN optical waveguidelayer 6 and the undoped InGaN optical waveguide layer 8 may be differentin composition provided favorable optical properties are ensured. Forexample, the In composition of the undoped InGaN optical waveguide layer8 may be lower than that of the undoped InGaN optical waveguide layer 6.It is also acceptable to use a material such as GaN different from theInGaN as the n-side optical waveguide layer and the p-side opticalwaveguide layer if it is appropriate.

The c-plane sapphire substrate used in any of the first to fifthembodiments may be replaced by SiC substrate, Si substrate, spinelsubstrate, substrate made of a thick n-type GaN layer, or the like, ifit is desirable. The GaN buffer layer may be replaced by an AlN bufferlayer or AlGaN buffer layer as well.

The first to fifth embodiments have been explained as applying thepresent invention to SCH-structured GaN compound semiconductor lasers.However, the invention is also applicable of course to DH (doubleheterostructure) structured GaN compound semiconductor lasers and evento GaN compound light emitting diodes.

The AlGaN layer of the p-type AlGaN/GaN superlattice cladding layer,which is not doped with Mg in the first to fifth embodiment, may be alsodoped with Mg. Alternatively, Mg may be doped into the AlGaN layerwithout doping Mg into the GaN layer.

Further, if appropriate, the p-side cladding layer may be made of anundoped or n-type first layer and a p-type second layer, and at the sametime, the n-side cladding layer may be made of an undoped or p-typefirst layer and an n-type second layer.

As described above, according to the invention, since the p-sidecladding layer is made of the undoped or n-type first layer and thep-type second layer doped with a p-type impurity, which are stackedsequentially from nearer to remoter from the active layer, it ispossible to reduce the thickness of the p-type layers having highspecific resistance values and causing an increase of the operationvoltage as thin as possible and thereby reduce the operation voltage ofthe semiconductor light emitting device while keeping a thickness of thep-side cladding layer necessary for ensuring a favorable light field anda favorable optical property. Since a sufficient distance can beprovided between the active layer and the second layer, diffusion of thep-type impurity of the second layer into the active layer anddeterioration of the active layer thereby can be prevented. Furthermore,especially when the second layer includes the p-type third layer havinga larger band gap than the second layer, the third layer can preventover flow of electrons injected to the active layer.

Furthermore, since the thickness of p-type layers in opposite sides ofthe ridge is limited within 0 to 100 nm, or the bottoms of the portionin opposite sides of the ridge are deeper than the boundary between thefirst layer and the second layer, the current injected during operationof the semiconductor light emitting device can be effectively preventedfrom leakage outside the ridge, and it contributes to attaining a muchhigher characteristic temperature than existing ones and realizingremarkably excellent temperature characteristics.

Furthermore, since growth of particular layers containing In is carriedout in the carrier gas atmosphere containing substantially no hydrogenand containing nitrogen as its major component, separation of In fromlayers containing In, such as the active layer, can be preventedeffectively, and deterioration of the active layer can be prevented,thereby improving reliability and lifetime of semiconductor lightemitting devices.

Furthermore, since the distance between the active layer and the nearestp-type layer doped with the p-type impurity is at least 50 nm, diffusionof the p-type impurity from the p-type layer to the active layer can bereduced significantly, and deterioration of the active layer can beprevented, thereby improving reliability and lifetime of semiconductorlight emitting devices.

Furthermore, since the n-side cladding layer is made of the undoped orp-type first layer and the n-type second layer doped with an n-typeimpurity, which are stacked sequentially from nearer to remoter from theactive layer, it is possible to minimize the thickness of n-type layerswith high specific resistance values causing an increase of theoperation voltage and thereby reduce the operation voltage while keepingthe n-side cladding layer thick enough to obtain a good light field forthe semiconductor light emitting device and thereby obtain favorableoptical properties. Additionally, since a sufficient distance can beprovided between the active layer and the second layer, diffusion of then-type impurity of the second layer into the active layer anddeterioration of the active layer thereby can be prevented.

Furthermore, since the thickness of n-type layers in opposite sides ofthe ridge is limited within 0 to 100 nm, or the bottoms of the portionin opposite sides of the ridge are deeper than the boundary between thefirst layer and the second layer, leakage of the current injected duringoperation of the semiconductor light emitting device outside the ridgecan be prevented effectively, and a much higher characteristictemperature than existing ones can be attained and remarkably excellenttemperature characteristics can be realized.

1. A semiconductor light emitting device made by using nitride III-Vcompound semiconductors, which has a structure interposing an activelayer between an n-side cladding layer and a p-side cladding layer,comprising: the p-side cladding layer including an undoped or n-typefirst layer and a p-type second layer doped with a p-type impurity whichlie in this order from one side nearer the active layer, and the secondlayer including a third layer having a larger band gap than the secondlayer.
 2. The semiconductor light emitting device according to claim 1wherein an n-side optical waveguide layer is interposed between then-side cladding layer and the active layer, and a p-side opticalwaveguide layer is interposed between the p-side cladding layer and theactive layer.
 3. The semiconductor light emitting device according toclaim 1 wherein the second layer of the p-side cladding layer has athickness in the range larger than 0 nm and not exceeding 550 nm.
 4. Thesemiconductor light emitting device according to claim 1 whereinthickness of the second layer of the p-side cladding layer is in therange from 390 nm to 550 nm.
 5. The semiconductor light emitting deviceaccording to claim 1 wherein thickness of the first layer of the p-sidecladding layer is in the range larger than 0 nm and not exceeding 500nm.
 6. The semiconductor light emitting device according to claim 1wherein thickness of the first layer of the p-side cladding layer is notthinner than 50 nm.
 7. The semiconductor light emitting device accordingto claim 1 wherein thickness of the first layer of the p-side claddinglayer is in the range from 50 nm to 400 nm.
 8. The semiconductor lightemitting device according to claim 1 wherein the first layer of thep-side cladding layer has a superlattice structure.
 9. The semiconductorlight emitting device according to claim 1 wherein the p-side claddinglayer has a super lattice structure. 10-12. (CANCELLED)
 13. Thesemiconductor light emitting device according to claim 1 whereindistance between the active layer and the second layer of the p-sidecladding layer is not less than 20 nm.
 14. The semiconductor lightemitting device according to claim 1 wherein distance between the activelayer and the second layer of the p-side cladding layer is in the rangefrom 100 nm to 180 nm.
 15. The semiconductor light emitting deviceaccording to claim 1 wherein at least one set of combined layersdifferent in band gap or lattice constant exists between the activelayer and the second layer of the p-side cladding layer.
 16. Thesemiconductor light emitting device according to claim 1 wherein atleast one layer of superlattice structure made of layers different inatomic composition ratio exists between the active layer and the secondlayer of the p-type cladding layer.
 17. (CANCELLED)
 18. A semiconductorlight emitting device made by using nitride III-V compoundsemiconductors, which has a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer,comprising: the p-side cladding layer including an undoped or n-typefirst layer and a p-type second layer doped with a p-type impurity inthis order from one side nearer to the active layer, and the first layerhaving a thickness not thinner than 50 nm.
 19. The semiconductor lightemitting device according to claim 18 wherein the second layer of thep-side cladding layer has a thickness in the range larger than 0 nm andnot exceeding 550 nm.
 20. The semiconductor light emitting deviceaccording to claim 18 wherein thickness of the second layer of thep-side cladding layer is in the range from 390 nm to 550 nm.
 21. Thesemiconductor light emitting device according to claim 18 whereinthickness of the first layer of the p-side cladding layer is in therange from 50 nm to 400 nm.
 22. The semiconductor light emitting deviceaccording to claim 18 wherein distance between the active layer and thesecond layer of the p-side cladding layer is not less than 20 nm. 23.The semiconductor light emitting device according to claim 18 whereindistance between the active layer and the second layer of the p-sidecladding layer is in the range from 100 nm to 180 nm.
 24. Asemiconductor light emitting device having a structure interposing anactive layer between an n-side cladding layer and a p-side claddinglayer, comprising: the p-side cladding layer including an undoped orn-type first layer and a p-type second layer doped with a p-typeimpurity in this order from one side nearer to the active layer, and thefirst layer having a thickness not thinner than 50 nm.
 25. Thesemiconductor light emitting device according to claim 24 wherein thesecond layer of the p-side cladding layer has a thickness in the rangelarger than 0 nm and not exceeding 550 nm.
 26. The semiconductor lightemitting device according to claim 24 wherein thickness of the secondlayer of the p-side cladding layer is in the range from 390 nm to 550nm.
 27. The semiconductor light emitting device according to claim 24wherein distance between the ative layer and the second layer of thep-side cladding layer is not less than 20 nm.
 28. The semiconductorlight emitting device according to claim 24 wherein distance between theactive layer and the second layer of the p-side cladding layer is in therange from 100 nm to 180 nm.
 29. A semiconductor light emitting devicemade by using nitride III-V compound semiconductors, which has astructure interposing an active layer between an n-side cladding layerand a p-side cladding layer and includes a ridge structure, comprising:the p-side cladding layer including an undoped or n-type first layer anda p-type second layer doped with a p-type impurity in this order fromone side nearer to the active layer, and the second layer including athird layer having a larger band gap than the second layer; and p-typelayers in opposite sides of the ridge having a thickness in the rangefrom 0 to 100 nm.
 30. The semiconductor light emitting device accordingto claim 29 wherein p-type layers in opposite sides of the ridge have athickness in the range from 0 to 50 nm. 31-52. (CANCELLED)
 53. Asemiconductor light emitting device composed of nitride III-V compoundsemiconductors and having a structure interposing an active layerbetween an n-side cladding layer and a p-side cladding layer,comprising: distance between the active layer and one of p-type layersdoped with a p-type impurity nearest to the active layer being not lessthan 50 nm.
 54. The semiconductor light emitting device according toclaim 53 wherein the distance between the active layer and the p-typelayer is not less than 60 nm.
 55. The semiconductor light emittingdevice according to claim 53 wherein the distance between the activelayer and the p-type layer is not less than 100 nm.
 56. Thesemiconductor light emitting device according to claim 53 wherein thedistance between the active layer and the p-type layer is in the rangefrom 50 to 500 nm.
 57. The semiconductor light emitting device accordingto claim 53 wherein the distance between the active layer and the p-typelayer is in the range from 100 to 200 nm.
 58. The semiconductor lightemitting device according to claim 53 wherein the distance between theactive layer and the p-type layer is in the range from 65 to 230 nm. 59.The semiconductor light emitting device according to claim 53 whereinthe distance between the active layer and the p-type layer is in therange from 70 to 125 nm.
 60. The semiconductor light emitting deviceaccording to claim 53 wherein the distance between the active layer andthe p-type layer is in the range from 90 to 110 nm.
 61. Thesemiconductor light emitting device according to claim 53 wherein thep-type layer nearest to the active layer has a larger band gap than thatof the p-side cladding layer.
 62. The semiconductor light emittingdevice according to claim 53 wherein at least one layer different incomposition from the active layer and the p-side cladding layer isinterposed between the active layer and the p-side cladding layer.63-64. (CANCELLED)
 65. A semiconductor light emitting device having astructure interposing an active layer between an n-side cladding layerand a p-side cladding layer, comprising: the n-side cladding layerincluding an undoped or p-type first layer and an n-type second layerdoped with an n-type impurity in this order from one side nearer to theactive layer, and the first layer having a thickness not smaller than 50nm. 66-67. (CANCELLED)